In a turbojet engine high-pressure turbine, the guide vane assembly is currently assembled by being fastened with the bottom of the casing, also called the “line of the internal casing.” Hereinafter, we will designate the line of the internal casing as being the assembly of structural elements supported or fixed directly to the internal casing of the turbine. Similarly, the expression “line of the external casing” will be used to refer to the assembly of structural elements supported or fixed directly to the outer turbine casing. Several fastening solutions have already been provided. They can be divided into essentially two categories: those commonly used requiring bolting as the means for fastening to the line of the internal casing, like that described in patent application EP 1 369 552, and that using other fastening means such as pins.
Such solutions using pins are for example described in patent applications FR 2 189 632 and EP 0 513 956.
One solution with a pin currently used by the applicant is shown in FIG. 1.
The designations “upstream” and “downstream” are used in relation to the flow of gas (from left to right in FIG. 1). Likewise, the terms “external,” “outer,” “internal,” and “inner,” “azimuthal” are used in relation to the position of the elements relative to the turbine shaft (situated at the bottom in FIG. 1). Thus an azimuthal position corresponds to an azimuth angle relative to the axis of rotation of the turbine shaft. FIG. 1 shows that the high-pressure guide vane assembly includes a sector defining a row of stationary flow-stabilizing vanes 1 placed upstream of the row of mobile vanes 2 of the high-pressure turbine. The inner edge 10 of a sector 1 is fastened to a so-called inner cone part 30 of the line of the internal casing 3 of the turbine via pins 4. This line of the internal casing 3 in particular comprises the guide vane casing 31. The outer edge 11 of a sector 1 bears axially against an annular part 50 that supports the mobile vanes 2 and that is fixed directly to the external casing 5 of the turbine. Owing to this assembly (axial bearing of the outer edge and fastening by pin of the inner edge), the stationary guide vanes 1 can, during operation of the turbine, tilt in the downstream or upstream directions, by several degrees with the aim of recovering the differential expansions likely to occur between the external casing 5 and the internal casing 3. Moreover, such an assembly makes it possible not to create excessive stresses and to guarantee sealing. During operation of the turbine, under the thrust of the gases, the stationary vanes 1 of the guide vane assembly bear axially on two zones symbolized by the ellipses, an inner zone Z1 and an outer zone Z2 with a more or less balanced distribution of the stresses. In other words, half of the thrust forces of the stationary guide vanes 1 are applied in zone Z1, the other half in zone Z2.
Thus, regardless of the fastening solution currently used to assemble the turbine guide vane assembly, and in particular that with pins used by the applicant, it is necessary to provide for sufficient dimensioning both of the line of the internal casing and the line of the external casing, to be able to react the stresses applied. Such a dimensioning must be accompanied by a given mass of the extensions of the internal and external casing, in particular the guide vane casing, which can be significant.
The aim of the invention is then to propose a solution that makes it possible to reduce the mass of the guide vane casing of a turbine, by reducing or even eliminating the forces applied on the line of the internal casing, during operation by the gas thrust.
In other words, the aim of the invention is to produce a turbine guide vane assembly making it possible to have all of the thrust forces applied on the line of the external casing and to recover the axial differential expansions likely to occur between the line of the external casing and the line of the internal casing.